Carbohydrates and their compounds have long been used in different areas. However, there continues to be a need to develop new carbohydrate-based compounds, which are distinguished by improved properties such as an increased surface activity.
The linear polydisperse carbohydrate, inulin, consists of a chain of .beta.-2-1-linked furanoid fructose units, which is terminated at the reducing end by an .alpha.-D glucose molecule. It occurs in composites, such as chicories, Jerusalem artichoke, dahlias and artichokes as well as in other types of plants, in which it serves as a storage material. It is isolated in economically significant amounts from chicories and Jerusalem artichokes. Depending on the type of plant and on the harvesting time, inulin has different molecular weight distributions and different average chain lengths between 8 and 25. The size of individual molecules ranges, in general, from 5 to 50 monosaccharide units per chain. There are, however, native inulins having an average chain length greater than 25 and correspondingly longer individual chains. Industrially, inulin is used primarily in the food sector for such purposes as the production of diabetic bread and fructose syrup.
Of the known carbohydrate esters based on polysaccharides, only starch and cellulose esters are used industrially. Starch esters, particularly the acetates, are used as sizing agents in the textile area, as surface glue in the paper industry, as thickeners in the film and fiber industry as well as in the food area and for molding. Of the cellulose esters, the synthesis of which is very costly because of the difficulty of dissolving the starting material, the acetates and their mixed esters with propionate and butyrate are of industrial interest. Of the low molecular weight carbohydrate esters, sucrose esters are particularly used, especially the acetates and the mono-fatty acid and di-fatty acid esters. Sucrose acetates and mixed esters with a high degree of substitution are used as bleaching agent activators and as plasticizers or softeners. Monoesters of sucrose and fatty acids are used as surfactants in detergents and as emulsifiers.
Carbohydrate esters can be synthesized in various ways. In solvent methods, the carbohydrate, in the presence of a basic catalyst in a solvent such as dimethylformamide or dimethyl sulfoxide, is reacted with methyl esters of fatty acids. In microemulsion methods, the fatty acid ester is dispersed in a solution of the carbohydrate by means of an emulsifier, for example, using the corresponding alkali salt of the fatty acid. The solvent is removed before the actual reaction. Finally, transesterification can take place directly in the melt of the carbohydrate and the fatty acid ester employing basic catalysis. Conducting the reaction of these known methods and working up the compounds is expensive. The reaction parameters of pressure and temperature must frequently be varied. In order to isolate the product, several extraction and distillation steps are required. Furthermore, in view of the high thermal stress on the products, there is danger of discoloration.
Little is known about the synthesis and use of inulin esters. Japanese patent No. 63,287,710 describes the peracetylation of the inulin chain in dimethylformamide/pyridine. Pringsheim et al., Chem. Ber. (1921), 54, 1281, describe the peracetylation of the inulin chain in pyridine. The peracetate shows adhesive properties, is water resistant and is therefore proposed for use in the cosmetics area. Schacht et al., Journal of Controlled Release, (1985), 2, 245, describe the use of succinoylated inulin as a carrier material for pharmaceutical products.
The compounds described are distinguished in that they possess only a slight surface activity or are difficult to synthesize. Surfactants, synthesized from petrochemicals, have the disadvantage of limited availability, and their synthesis, moreover, is environmentally compatible only to a limited extent.
The technical problem for which the present invention provides a solution is to make available surface active carbohydrate compounds which overcome the aforementioned disadvantages and, in particular, are easily synthesized and environmentally compatible and, furthermore, because of their surface active properties, are suitable for a plurality of uses.